Altitude Above the Height of the Ocean
This page is the CodyCross answer for the clue below from Top Secret, Group 2083, Puzzle 1 (Field Operative).
Question is: Altitude Above the Height of the Ocean
and the answer is: SEALEVEL
Word Meaning:
SEA LEVEL — The nominal height of the surface of the oceans above which heights of geographical features and aircraft flight levels are measured.
Definitions from Wiktionary.